1. Field of the Invention
The present invention relates to a magnetoresistive device adapted to read the magnetic field intensity of magnetic recording media or the like as signals, and a thin-film magnetic head comprising that magnetoresistive device as well as a head gimbal assembly and a magnetic disk system, one each including that thin-film magnetic head.
2. Explanation of the Prior Art
A thin-film magnetic head is built up of a reproducing head having a reading magnetoresistive device (MR device) and a recording head having a writing induction type electromagnetic device.
A typical construction of part of the MR device includes a multilayer structure made up of an anti-ferromagnetic layer/first ferromagnetic layer/non-magnetic intermediate layer/second ferromagnetic layer.
The first ferromagnetic layer is also called a fixed magnetization layer because its direction of magnetization remains fixed by the antiferromagnetic layer adjacent to it. By contrast, the second ferromagnetic layer is referred to as a free layer because its direction of magnetization changes by way of sensitive reaction with an external magnetic field change.
A lower electrode and shield layer and an upper electrode and shield layer (hereinafter often called the shield layers for short) are provided such that the aforesaid multilayer MR device is sandwiched between them from above and below, so that leaking magnetic fluxes from adjacent recorded data can be cut off.
The shield layers located above and below the multilayer MR device are each made of a soft magnetic thin film, and one each is generally formed in such a way as to have a closure domain structure with an easy axis of magnetization in the same direction as the track width direction of the MR device. Here, if the domain structures of the shield layers are not stably formed with variations per head, then there are also variations in the bias state applied to the MR device (especially a bias applied to the free layer), which may otherwise give rise to a problem of offering an obstacle to improvements in production yields.
In association with an increasing magnetic recording density, it is increasingly required for the MR device to be much narrower than ever before in terms of track width and read gap. As the read gap grows narrower, it causes the distance between the shield layers and the free layer forming the MR device portion to decrease drastically, letting the shield layers have strong influences on the bias state of the MR device portion. Specifically, if there is a change in the domain structures of the shield layers due to an external magnetic field, it could bring about an output fluctuation of the MR device. That is, the resistance to an external magnetic field (magnetic field resistance) could get worse.
To make the domain structure of the shield layers stable, JP(A)8-212521 discloses a technique of providing a domain control layer for the stabilization of the domains for the shields. Specifically, the publication sets forth a method wherein an antiferromagnetic film or hard magnetic film is formed for the magnetic shields thereby achieving a single domain structure having one single direction of magnetization.
Similar effects are also achieved by the method of JP(A)8-169023 showing that the magnetic shield is made up of a multilayer film structure comprising a multilayer structure of a soft magnetic film and a nonmagnetic film.
However, these methods are now found to have a problem with practical use, because they involve very intractable production processes. More exactly, the former has much difficulty in achieving a single domain for a shield layer of about 1 μm in thickness, using the exchange coupling of an antiferromagnetic film or hard magnetic film. The latter would be not very practicable, too, because of needing a lot more stacks for achieving a single domain.
JP(A)2007-242140 discloses a technique for configuring the planar shape of a shield portion in a reproducing head into an annular one to control the domain structure of the shield portion thereby reducing output fluctuations of the reproducing head under the influences of the shield and, hence, obtaining stabilized outputs.
As far as what is set forth in the aforesaid publication is concerned, control of the domain structure of the shield portion would be still less than satisfactory. Thus, there is a mounting demand for the development of a novel technique for holding back output fluctuations of the reproducing head under the influences of shields and, hence, obtaining stabilized outputs.
The situation being like such, the invention has been made for the purpose of providing a novel device structure capable of turning a shield layer of the order of a few thousands Å to a few μm into a single domain in a simplified yet stable manner and achieving a more stable domain structure so that output fluctuations of a reproducing head under the influences of shield layers can be kept more in check to allow the reproducing head to produce stabilized outputs.